Boiler burner for solid fuels of the biomass or tyre type and boiler comprising such burner

ABSTRACT

The invention relates to a burner for solid fuel such as biomass or tyres, that comprises a heating body in the shape of a cylinder ( 1,1′, 1 ′) with solid fuel supply means and means for the inlet of primary air ( 13, 13′, 13 ′) as oxidant, said cylinder being provided with a plate ( 3,3′,3 ′) in its lower part. The invention comprises placing the plate above the means for the inlet of primary air ( 13, 13′, 13 ′), wherein the plate has through holes and is arranged so as to receive the fuel without the fuel flowing therethrough, and said burner further includes inside said cylinder ( 1, 1′,1 ′) means for generating a negative pressure within the burner so as to generate a primary air circulation from the underside of the plate ( 3, 3′,3 ′) and through said plate and the fuel resting thereon up to a gas outlet duct ( 4, 4′, 4 ′) in the upper portion of said burner. Application in the combustion of biomass, tyres and the like.

The present invention concerns a boiler burner for solid fuels of biomass or tire type as well as a boiler containing such a burner.

The field of energy production from biomass has undergone great strides in recent years. In fact, the problems associated with the usual energy resources such as hydrocarbons, from the standpoint of the reduction of reserves as well as of the pollution generated or even quite simply their economic cost, have led to consideration of the use of biomass as an energy source.

The term biomass classically embraces all of the types of energy derived from the degradation of organic matter produced from solar energy transformed by the plants used either directly or after a methanization of organic matter (biogas) or new chemical conversions (biofuel).

The present invention is aimed in particular at the field of use of biomass as fuel feeding a boiler.

Thus, installations for production of energy from the combustion of fuels as highly varied as sawdust, logs, straw, plant wastes, forest byproducts or brush, corn cobs, coconuts, etc. are already well known.

The burner constituting the combustion chamber of the boiler brings together the fuel and the oxidant consisting of air for the purpose of combustion. This burner generally consists of a casing in which fuel is filled and air is admitted as oxidant.

A flame poorly fed with oxidant is long and smoky, for it seeks oxygen over its height. Thus, to generate circulation of air inside the burner in order to favor the flame, a fan is provided in the boiler, enabling the inlet of primary and secondary air and as often as possible, a fan is provided for outlet of the fumes at the top of the boiler. The presence of these fans can cause maintenance problems owing to their exposure to relatively high temperatures, those high temperatures being necessary for good combustion.

It could also be observed that, depending on the nature of the fuel, there was a more-or-less large occurrence of residues. Thus, when the fuel is wood-based, combustion generates almost no ash; while in the case of cereals, solid residues like cinders are formed on combustion.

To solve that problem of combustion residues, patent FR 2,880,407 proposed a heating device containing notably a burner with fragmented fuel such as cereals, adapted to permit the extraction of solid residues without outside human intervention and without interrupting operation of the heating device. Such a self-cleaning burner thus consists of a perforated casing, in which the top part contains upper and lower openings and the bottom part also contains an upper opening connecting with the lower opening of the top part, the bottom part being movably mounted between an operating position and a cleaning position in which its upper opening is directed downward, closing means being provided to close the lower opening of the upper part when the bottom part is shifted.

EP 0,882,201 also describes a boiler with continuous feed of granulated solid fuel, the combustion of which is optimized. Such a boiler has two superimposed stages: a lower one in which a tubular combustion chamber is located with a vertical extension into which means of fuel supply are fed and an upper one in which an exchanger and a smoke discharge pipe are located, the two stages connecting by means of a nozzle for exhaust of the flames out of the combustion chamber toward the exchanger under the effect of so-called primary air circulation means from the base of the combustion chamber and axially through its inner space to the smoke discharge pipe. The air circulation means consist of means of pressure reduction of the upper and lower stages downstream from the upper stage. Therefore, such a boiler has the advantage that the air circulating under the effect of the partial vacuum cannot follow any path other than that imposed on it by the means of pressure reduction in contrast to means of pulsation type. Such a boiler has a high output due to the optimization of combustion and removal of the heat produced, notably thanks to ascending air circulation means. These means are of standard turbine type.

However, outside that configuration in superimposed stages in order to generate air circulation, it is not possible to envisage other boiler configurations.

In DE 10 2004 051,685, a boiler is proposed with a combustion chamber in which wood chips are automatically pushed by an endless feed screw. The fresh air indispensable for combustion with oxygen arrives through a primary air duct under a heating grate or above in the combustion chamber. The heat released by combustion heats the water in the heating circuit through the walls of the tank and a system of pipes with combustion gases which transmit the heat only partially through the heating circuit. A combustion gas—primary air heat exchanger is provided in the combustion gas pipe above the combustion chamber. That exchanger acts as primary air reheating chamber. Inside the exchanger, numerous pipes are placed vertically from the bottom to the cover, the combustion gases traverse those pipes vertically as far as the stack and heat them. On the side walls opposite the heat exchanger, there is an inlet opening for the primary air and an outlet opening for the connecting pipe, making possible the supply of the primary air necessary for combustion. The primary air crossing horizontally from the inlet opening to the outlet opening is reheated on contact with the pipes containing the combustion gases. At the outlet opening, the reheated primary air passes through the pipe to the fuel combustion chamber of the boiler and a considerable improvement in degree of efficiency is attained with that intake of air associated with the heat. To attain the flow capacity necessary for combustion, a pneumatic conveyor is set up for intake of the primary air and removal of the combustion gases in the flow path. An axial fan is provided, being positioned between the heat exchanger and the stack and operates as exhauster on the flow path from the heat exchanger and boiler and as superpressure generator in the stack. This is, therefore, a bulky two-stage boiler.

In US 2003/0,097,969, an incinerator is proposed for the combustion of solid wastes such as husks. That incinerator comprises a furnace having peripheral walls extending vertically with a bottom part defining the main combustion chamber, an intermediate section above, defining an auxiliary combustion chamber, a cooling section above the intermediate section and a top section above the cooling section formed with a delivery of effluent for the discharge of combustion gases generated in the main and auxiliary combustion chambers. There is also a partition separating the combustion chambers and forming a channel in fluid communication with the two chambers. A supply unit comprising a feed motor makes it possible to deliver the solid wastes to the furnace. A space is arranged between the peripheral wall and a heat insulating shield extends all around the different sections, except for the top part and the effluent outlet. An air outlet in fluid communication with the space is provided in the peripheral wall of the heat insulating shield and is adjacent to the top part of the latter. A fan is placed downstream from that air outlet and on an air duct for introducing air, via the open lower end of the incinerator, in the space, air outlet and dryer, so that the air introduced is heated in the space by the flow of heat from the peripheral wall. In a dryer combined with the device, a temperature sensor is installed and generates electric signals corresponding to the temperature detected and is connected to a control unit making it possible to regulate the feed of solid waste from the furnace via the motor according to the temperature of the dryer. A main fan is connected to the furnace by an air duct and makes it possible to deliver air to said furnace. The solid waste support plate is placed in the bottom section of the furnace and contains several holes affording passage of the ash which is brought to a bottom outlet by a wheel driven by a motor. A rack is rotary-mounted via a motor above the support plate in order to move the ash and to facilitate the drop of the ash via the holes and thus increase the combustion efficiency of the furnace.

Better air circulation is indispensable for good combustion of solid wastes. Good circulation of primary air can, as described in the above-mentioned documents, be obtained by means of fans. However, these fans are always used outside the combustion chamber or burner, for, in fact, it is not possible to position them inside that burner owing to the heat. In general, these fans are positioned either outside the combustion chamber (US 2003/0,097,969) or above said chamber after a heat exchanger part in front of the stack (DE 10 2004 051,685). Owing to the temperature prevailing inside the burner, maintenance problems due to their exposure to high temperature are avoided by those arrangements. The presence of these fans also generates a space factor and likewise limits the temperature rise inside the burner, since beyond a certain temperature threshold, those fans risk being damaged, even if they are outside the burner.

The present invention, therefore, proposes a burner in which combustion is optimized so that it can be fed with different types of biomass, while having optimized performance characteristics which can be integrated in a boiler without the latter needing to have two superimposed stages. A boiler of different architecture can thus be made with such a burner, notably at the exchanger level.

In addition, the present invention is aimed at a burner in which a solid fuel can be used, such as the biomass consisting of cereals, sunflower or rapeseed residues, granulated beets, wood pellets, shredded wood, etc., but which also makes it possible to use other fuels such as worn tires, that is, a burner in which the combustion temperature can be very high.

To avoid the problems associated with solid residues resulting from the combustion of certain kinds of biomass, as previously mentioned, a burner is proposed in which the combustion generates much less of these residues, particularly on combustion of cereals, which therefore necessitates less frequent cleaning.

For that purpose, the object of the invention is a burner of solid fuel, such as biomass and tires, comprising a heating body in the form of a cylinder equipped with solid fuel feed means and primary air inlet means as oxidant, said cylinder being provided at its lower part with a plate, that plate having through holes arranged to receive the fuel without the fuel flowing through, and said burner further containing inside said cylinder means generating a partial vacuum in the burner, so as to create a primary air circulation from the bottom of said plate through the latter and the fuel resting on top up to a gas outlet duct in the upper part of said burner.

Thus, the partial vacuum generated inside the heating body of the burner by the means located in the cylinder itself and, therefore, in the combustion chamber itself and no longer outside the latter upstream and/or downstream, as was the case in the documents previously cited, makes it possible to draw air from the bottom of the burner across the wall provided with through holes and, therefore, to accelerate the air through the burner and to convey the gases formed at the base of the cylinder by raising the temperature up to the outlet pipe of the burner in the upper part of said cylinder, the cylinder being high enough to separate the gases from the unburned particles, which can redescend to the bottom wall. Considerably improved air circulation is, therefore, obtained inside the burner with a temperature rise inside the burner resulting in almost residue-free combustion.

Furthermore, at the bottom plate, a scraping means is provided which also serves to level the height of fuel so that the air can pass evenly, the scraping means serving to poke the surface of the fire, which further accelerates it. That scraping means is kept at a certain height to prevent the fire from being extinguished.

The fuel is preferably fed from the top of the burner by distribution means such as a rotary feeder. That fuel distribution is thus much more regular than with an endless screw and, furthermore, offers the advantage of taking place without passage of air from outside the burner toward inside. It is thus capable of a measured or calibrated flow of fuel.

It is thus possible to obtain residues amounting to less than 1% of the fuel used. This results in a high gas production.

Also, according to one particularly advantageous embodiment of the invention, the means making it possible to reduce the pressure inside the burner and housed in said cylinder of the burner consist of compressed air supply means positioned in the upper part of the cylinder and creating a partial vacuum by way of a Venturi effect, the compressed air supply means being directed, furthermore, toward the gas outlet pipe.

The partial vacuum thus created inside the burner according to the invention is advantageously much greater than a partial vacuum created with an outside fan and even greater than that obtained by the natural draft of a stack. Furthermore, the compressed air directly admitted into the cylinder is hot and therefore does not create any cold point which might impair operation.

Accordingly, these compressed air intake means are positioned so that the air from that “Venturi effect” also supplies the oxidant necessary for combustion of the gases in the outlet pipe of the burner. In fact, the compressed air and the “Venturi effect” generate an intense thrust making possible the outlet of gases at the top of the boiler.

The “Venturi effect” converts the internal partial vacuum of the combustion pot (cylinder) into pressure in the outlet pipe of the burner by a few centimeters and without mechanical parts by means of a simple jet. That pressure conversion is possible only because of the confined space of the burner and the energy associated with the compressed air. That concentration and the oxidant supply at the outlet pipe generate a high-temperature flame of between 850° C. and 1000° C. depending on the fuel, which finalizes the combustion.

The compressed air is supplied very advantageously by means of a jet fed by a compressor and the compressed air pressure is regulated simply by means of a pressure reducing valve, which makes it possible to guarantee optimal combustion regardless of the fuel used.

This internal partial vacuum created in the heating body of the burner ensures safety in fire propagation, notably in relation to the fuel supply.

Furthermore, a burner according to the invention necessitates the presence of very little fuel, like, for example, 100 grams of fuel for a 30 Kw burner. A quick stop is thereby guaranteed, making easier control possible.

A burner according to the invention, therefore, proposes rapid combustion in a very hot confined space with very great air circulation. That concentration of combustion in the burner alone generates much higher heat than in a standard burner with a fan or natural draft wherein the air circulation takes place on partial vacuum or pressure (pulsated air).

The outlet of the gas-air mixture likewise acquires an acceleration and a compression associated with the “Venturi” effect in a confined space.

A burner according to the invention, because of its even flow of fuel and air, does not require an overly complex regulating system, particularly not necessitating complex electronic control means. The “Venturi effect” occurring in the burner makes possible a greater addition of air in a more constricted (and therefore hotter) space, which makes pyrolysis possible at the outlet of the burner (blowtorch effect) in contrast to a fan which has a lower speed and a greater output for a same rate of flow.

According to a first particular embodiment, the burner contains an outer casing which defines with the cylinder a compartment constituting means of air flow to the primary air inlet means situated under the bottom plate of the burner. These air inlet means consist simply of a space provided under the bottom plate of said burner into which the air is fed, said space being defined by said outer casing extending under the cylinder. The air circulating in the annular compartment surrounding the cylinder is advantageously reheated, which further favors combustion on its entry into the burner.

In this embodiment, it can be envisaged that the burner will be outside the boiler.

As a variant, the space under the bottom plate constituting the primary air inlet means can be defined by the cylinder itself or the boiler, air inlet means emptying into that space and bringing air from the lower part of the boiler. These air inlet means can be concentric to the exhaust gas outlet pipe of the boiler, so that a heat exchange takes place, enabling the reheating of the primary air before its inlet in the burner, which promotes combustion and cooling of the exhaust gases before their outlet from the boiler. The heating effect is thus optimized.

According to another embodiment of the invention, the air inlet means also consist of a space created under the bottom place of said burner, into which the air is fed, the primary air inlet means consisting of a pipe extending preferably centrally in the cylinder from the upper part of the latter and entering under the plate of said burner through a central opening of sufficient section for the primary air. The primary air moving in that central pipe inside the burner is considerably reheated, which promotes combustion.

The invention also concerns a boiler containing a burner according to the invention. This boiler can, therefore, contain an “all or nothing” operating central burner, the burner being fed continuously in heating phase. Such a boiler is preferably of the vertical cylindrical type, the burner being housed in the upper central part.

A burner according to the invention and the boiler incorporating it can very advantageously utilize as solid fuels cereals, granulated beets, wood pellets, shredded wood, rapeseed oil cakes and the like, and also shredded tires.

A boiler according to the invention requires few moving parts and, therefore, few motors and little maintenance. The compressor is preferably outside the boiler and is therefore not subject to temperature differences.

Thus, such a boiler also makes it possible to use the rapeseed wastes (oil cakes) resulting from pressing of the rapeseed, for example, to manufacture the oxidant.

For shredded wood, calibration is necessary, since overly large pieces of wood are harmful to operation of the grinder.

In the case of tires then, it is arranged for the burner to contain, at the gas outlet pipe, means of generating a flame, such as propane or butane supply means, which make it possible to burn the gases on their exhaust from the burner and very advantageously avoid any odor of burnt rubber. Preferably, the flame generating means are adjustable over a given range.

Therefore, the burner according to the invention makes it possible to use a solid fuel such as biomass, whatever that biomass may be, but also makes it possible to envisage the use of shredded worn tires as solid fuel without generating any of the usual disadvantages, particularly unpleasant odors.

In particular, in order to adjust fuels such as tires and rapeseed residues to sizable gas expansion, a larger jet makes it possible to supply more compressed air at the outlet of the burner without increasing the partial vacuum inside said burner. Consequently, such a jet makes it possible to burn at the outlet the extra gas generated, without altering the partial vacuum inside the burner, particularly in its lower part, and without thus altering the air circulation.

Such a burner makes it possible to have a gas-water reverse flow (outlet of gases from the burner in the highest part of the boiler—outlet of cooled gases in the bottom part, therefore, with arrival of colder water).

Furthermore, on stopping, the boiler has a hot-air balloon effect, and the hot gases cannot escape. As convection cannot take place in the stack, losses are considerably reduced.

In addition, such a burner according to the invention can also be set up so that it can be positioned on a fuel or wood type standard boiler door in order to transform the latter. It will then preferably have a low capacity of approximately 10 to 15 Kw.

The invention will now be described more in detail with reference to the drawings in which:

FIG. 1 represents a longitudinal cutaway view of a first embodiment of a burner according to the invention;

FIG. 2 represents a cutaway view of FIG. 1 at line A-A;

FIG. 3 represents a longitudinal cutaway view of an example of a boiler with a burner according to FIG. 1;

FIG. 4 represents a longitudinal cutaway view of another example of a boiler with a burner according to FIG. 1;

FIG. 5 represents a longitudinal cutaway view of a second embodiment of a burner according to the invention;

FIG. 6 represents a cutaway view of a part of another example of a boiler with a burner according to FIG. 5;

FIG. 7 represents a cutaway view of the boiler along cutaway line B-B;

FIG. 8 represents a cutaway view of a burner according to the invention positioned on a standard boiler; and

FIG. 9 represents a cutaway view of FIG. 8.

The burner according to the invention comprises a cylinder 1 made of refractory material such as refractory stainless steel and an outer casing 1 a. This refractory stainless steel has the advantage of a narrow thickness. The thermal mass is therefore less, and the temperature for good combustion conditions can then be raised more rapidly than with a refractory material of greater mass.

In the upper wall 1 b closing the cylinder 1, a fuel feed opening is created. Across that opening, a fuel feed pipe 5 is engaged, connected to a fuel reserve 6 a through a rotary feeder 6 which ensures the regular fuel supply of the burner. The configuration of the feeder, reserve and pipe 5 enables the regular supply and even makes it possible to “measure and calibrate” this supply. The feeder can be linear or cylindrical, but it must above all never allow air to pass.

The cylinder 1 further contains a bottom wall 3 provided with through holes, the dimensions and through holes of which are chosen according to the power of the burner. In particular, this bottom wall 3 forming the bottom plate does not allow fuel to pass, but allows air to pass. This perforated bottom wall 3, a grate, for example, consists preferably of a refractory steel plate.

The cylinder 1 of the burner is surrounded by an outer casing 1 a that is parallel to said cylinder and extending cone shaped into the lower part of the latter.

The burner further contains primary air inlet means in the cylinder 1 or heating body. Those air inlet means 13 are positioned in the lower part of the burner under the bottom wall 3. The air is brought in at the inlet means 13 consisting of the cone-shaped space defined between the bottom wall 3 and the outer casing 1 a surrounding the cylinder from the upper part of the burner and, therefore. from the boiler (see FIG. 3) via the annular compartment 1 c created between the cylinder 1 and said outer casing 1 a.

The burner further contains means making it possible to generate a partial vacuum inside said burner, those means consisting of compressed air distribution means 2 positioned in the upper part of the cylinder 1 of the burner.

That compressed air supply generates a Venturi effect in the upper part of the cylinder 1 which is thus pressure-reduced.

Owing to the partial vacuum created in the cylinder 1, the bottom wall with through holes 3 serves as a nozzle, the air coming out underneath being drawn in by the partial vacuum prevailing in the cylinder 1 and crossing the fuel resting overhead, the burner thus operating roughly like a forge.

Because of that partial vacuum, the gases formed at the base by the temperature rise are lifted to level of the Venturi effect V generated in the upper part of the cylinder 1 to the outlet pipe 4 of the burner, while the air from that Venturi effect supplies the oxidant necessary for combustion in the outlet pipe 4 of the burner.

A shaft 8, preferably tubular, is also provided inside the cylinder 1, extending across the upper wall of the cylinder to the combustion nozzle 3. That shaft 8 can be driven in rotation simultaneous with the rotary feeder 6, while its free end in the lower part of the cylinder 1 is equipped with scraping means 9 or a scraper which makes possible the regular dispersion of the fuel in the lower part of the cylinder 1 above the bottom wall 3.

This scraper 9 makes it possible to level the fuel, so that the air passing through the bottom wall 3 crosses the same thickness of fuel in order for the fire to be even over the whole surface of the burner.

This shaft 8 further contains, in the upper part outside the cylinder 1, an air inlet 8 a and possibly an air outlet in the lower part. The air coming in enables cooling of the shaft 8.

Secondary air inlet means in the form of a pipe 11, extending parallel to said shaft 8 and connected to the primary air feed means 1 c, are also provided. This pipe 11 enters the upper part of the cylinder 1 and ensures a continuous flame in upper part of the burner at the level of the Venturi effect.

On the side of the burner in the compartment 1 c, an electric resistor inserted in a ceramic is housed in a pipe 14 and ensures ignition of the fuel at the bottom of the burner. An air supply lower than in operating conditions is provided at the time of ignition. The air passing between the combustion pot (cylinder 1) and the outer casing 1 a of the burner is reheated for better combustion. That air has an adjustable rate of flow in order to be able to differentiate the precombustion-gasification from the post-combustion (more air at the level of the “Venturi effect” generates more partial vacuum).

When wood or sunflower is used as fuel, the combustion residues consisting solely of light ash are also sucked up by the Venturi effect and expelled from the burner through the outlet pipe 4 with the gases. That outlet pipe 4 in which pyrolysis takes place must be long enough for the temperature of all the particles and the tar to be raised in order to burn them up, particularly with a view to meeting the standards in force.

The gases at the outlet of the burner (represented by black arrows in FIG. 3) are projected (cyclone effect) to turn around the burner, so that the particles are projected on the inner face 15 a of a wall 15 of the boiler, defining with the outer wall 18 of said boiler a compartment E in which the water flows (white arrows), being heated by heat exchange with the gases. The gases are then taken up at the lower part at outlets 16 provided at the center, once they are less hot and particle-free. The ashes drop by gravitation into a drawer 17 at the bottom of the boiler.

In the case of a fuel such as wheat, the ashes are encountered on the bottom plate or nozzle 3, like clinker. To enable cleaning of the burner, means for translation drive of the shaft 8 are provided in order to lower the scraping means 9 from its fuel mixer position to a position of contact with the combustion nozzle 3, so that the scraping means 9 will then serve to grind the residues in order to make them pass the through holes of the nozzle 3 into the ash box.

These drive means can notably consists of a jack, preferably pneumatic.

In the center of the drawer 17 placed at the bottom of the boiler to collect the ashes, a blocking means 19 is provided, which obstructs the outlet of the residues in clinker form. When the drawer 17 comes out, that “clinker” drops into the ashes.

When the fuel used consists of tire residues, the resulting metal parts are accumulated on the bottom wall 3. This bottom wall 3 is then preferably arranged to turn on a 90° axis(represented by a dotted line in FIG. 1) so that the metal waste will drop into the ash box 17.

In the boiler example represented in FIG. 4, the primary air inlet means at the bottom of the burner are placed at the bottom of the boiler and consist of a pipe 20 concentric to the gas outlets 16, which makes it possible to reheat the primary air, while cooling the exhaust gases before their outlet from the boiler. That pipe 20 enters the roughly cone-shaped lower part of the cylinder 1 under the bottom plate 3, constituting the primary air inlet means. The burner represented in the boiler of FIG. 4, therefore, does not have any outer casing 1 a defining an air inlet compartment. For the sake of clarity, some components of the burner of FIG. 1, such as the secondary air inlet means, are not represented in FIGS. 3 and 4, but can, of course, be present.

As with the burner of FIG. 1, the burner represented in FIG. 5 comprises a cylinder 1′. In the upper wall 1′b closing the cylinder 1′, a fuel feed opening is provided. Across that opening, a fuel feed pipe 5 is engaged, connected to a fuel reserve 6 a through a rotary feeder 6 which ensures the regular fuel supply of the burner. The feeder 6 can be linear or cylindrical, but it must above all never allow air to pass.

The cylinder 1′ further contains a bottom plate or grate 3′ having roughly the same characteristics as previously described.

The burner 1′ also contains means making it possible to generate a partial vacuum inside said burner, those means consisting of compressed air distribution means 2′ positioned in the upper part of the burner.

This compressed air feed generates a Venturi effect V in the upper part of the cylinder 1′, which is thus pressure-reduced.

Owing to the partial vacuum created in the cylinder 1′, the bottom wall with through holes 3′ serves as a combustion nozzle, the air coming out underneath being drawn in by the partial vacuum prevailing in the cylinder 1′ and crossing the fuel resting overhead. The burner thus operating roughly like a forge.

Because of that partial vacuum, the gases formed at the base by the temperature rise are lifted at the level of the Venturi effect V generated in the upper part of the cylinder 1′ to the outlet pipe 4′ of the burner, while the air from that Venturi effect V supplies the oxidant necessary for combustion in the outlet pipe 4′ of the burner.

The burner further contains primary air inlet means in the cylinder 1′ or heating body. These air inlet means 13′ consist of a space created under the plate or grate 3′. The means of primary air feed to said air inlet means consist of a pipe 130 extending into the cylinder 1′ from the upper wall 1′b of the latter and coming out under the grate 3′ in space 13′. In this way, the primary air circulating in the pipe 130 is reheated in the core of the cylinder 1′ and comes out in space 13′ considerably reheated, which promotes combustion.

A shaft 8′, preferably tubular, is also provided inside the cylinder 1′, extending across the upper wall of the cylinder 1′ in the pipe 130 to the combustion nozzle 3. This shaft 8′ can be driven in rotation simultaneous with the rotary feeder 6, while its free end in the lower part of the cylinder 1′ bears the grate 3′, which is thereby likewise driven in rotation at a speed identical to that of the fuel supply 6, so that the fuel is very evenly distributed over the latter. With the shaft 8′ extending in said pipe 130, the air intake is thus less hot. This shaft 8′ turns the grate 3′, which can thus be driven in rotation.

A scraping means 9′ or scraper is rotary-mounted in the cylinder 1′, so that the rotation of the grate 3′ in relation to said scraper 9′ makes it possible to spread the fuel evenly in the lower part of the cylinder 1′ on the aforesaid bottom wall 3′.

This scraper 9′ makes it possible to level the fuel so that the air passing through the bottom wall 3′ crosses the same thickness of fuel in order for the fire to be evenly distributed over the entire surface of the burner.

The grate 3′ preferably has a diameter roughly corresponding to the internal diameter of the cylinder 1′, while the space 13′ provided under the grate 3′ has a greater diameter. The grate 3′ can preferably be lowered into said space 13′, thus freeing the periphery of the grate 3′.

When the grate 3′ is lowered, the scraper 9′ is also lowered with a greater width, so that it abuts said grate 3′ in the scraping position of the latter. The rotation of the grate 3′ enables the scraper 9′ to be rotated, but inclined in relation to the axis of rotation of the grate 3′, to scrape said grate 3′ which turns and to remove the residues thus eliminated on the periphery of the grate 3′ and falling into the space 13′.

The bottom 23 of the space 13′ is mounted pivoting on a pin 24, so as to open when the shaft 8′ resting on said bottom 23 is lowered in order to lower the grate 3′. The residues falling into the space 13′ are thereby discharged by gravity into an ash drawer of the boiler provided under said space 13′.

This lowering of the shaft 8′, grate 3′ and scraper 9′ can be carried out by means of offset pins. This shaft 8′ contains, in fact, at its upper part outside the cylinder 1′, a pin 21 extending crosswise to said shaft 8′. This pin 21 is mounted pivoting at one end 21 a, which is lower than a pivot point 21 b of this pin 21 on the shaft 8′, lower in turn than the opposite end 21 c of the pin 21 mounted at the end of the rod of a jack 22 that is preferably pneumatic and connected to the compressor of the compressed air inlet means. As for the scraper 9′, it is borne by a shaft 9 a′ extending parallel to shaft 8′ and the end of which is mounted pivoting at 21 d on the pin 21 in proximity to the end 21 c.

When the jack 22 is actuated, the rod 22 a of said jack 22 forces back the pin 21 and, therefore, lowers the shaft 9 a′ bearing the scraper 9′, as well as shaft 8′, the scraper 9′ being lowered with a greater amplitude owing to the structure created.

Secondary air inlet means in the form of a pipe 11′ connected to the primary air feed means 130 are also provided. This pipe 11′ enters the upper part of the cylinder 1′ and ensures a continuous flame at the top of the burner at the level of the Venturi effect V.

On the side of the burner, an electric resistor inserted in a ceramic is housed in a pipe 14′ and ensures ignition of the fuel at the bottom of the burner. An air supply lower than in operating conditions is provided at the time of ignition. Air is propelled around that resistor and comes from a compressed air jet timed by a solenoid valve.

A boiler equipped with such a burner is represented in FIGS. 6 and 7. The gases at the outlet of the burner are projected from a bent gas outlet pipe 4′ (cyclone effect) so as to turn around the burner, in order for the particles to be projected on the inner face 50 a of a wall 50 of the boiler, defining with an outer wall 60 of said boiler a compartment E in which the water flows, being heated by heat exchange with the gases (1^(st) stage). The gases are then taken up at the bottom, once they are less hot and particle-free, by a gas outlet 40.

The boiler further contains a second stage of reheating 30 of the return water from heating (black arrows) with the cooled gases of the first stage.

This T-shaped gas outlet 40 makes it possible to take cooler gases at the bottom of the main body of the boiler. The vertical part 41 of the T-piece makes it possible to cool the cooler gases with water at a lower temperature. This T-shaped gas outlet 40 enables the possible particles originating from combustion to be separated.

A cleaning plug makes it possible to discharge the residues and channel the low temperature condensation. The inlet end 42 of the gas outlet pipe 40 at the bottom of the main body is beveled in order not to carry away the particles descending into the exhaust duct 41. A pipe 31 makes it possible to take up the water at the top of the second heating body and to inject it at the bottom of the main body on the other side of the partition 50.

In FIGS. 8 and 9, the burner 1″ is represented according to the invention, set up to be positioned on the door P of a standard type boiler. Such a boiler 1″ is fed with fuel by means of a feeder 6″ equipped with a hopper 6 a″ positioned in the boiler and by an inclined pipe 5″ connected to the burner 1″ through the door P. A deflector 5 a″ positioned at the end of the pipe 5″ makes possible a distribution on the bottom plate 3″ of the burner 1″.

The pipe 14″ containing the ignition resistor is placed horizontally, while the primary air inlet means 13″ consists of a space under the bottom plate 3″, provided with a bottom 23″.

The primary air feed means 130″ consist of a chamber provided between the door of the boiler and the burner 1″, so that this air is reheated before entering the inlet means 13″. Secondary air inlet means in the form of a pipe 11″ connected to the primary air feed means 130″ are also provided. This pipe 11″ enters the cylinder 1″ and ensures a continuous flame in the upper part of the boiler at the level of the Venturi effect V generated by the compressed air distribution means 2″ positioned in the upper part of the burner at the level of the gas outlet pipe 4″.

The invention is, of course, not limited to the working examples given, but also includes all the variants coming within the scope of protection defined by the claims. 

1. Burner of solid fuel, such as biomass and tires, comprising a heating body in the form of a cylinder equipped with solid fuel feed means and primary air inlet means as oxidant, said cylinder being provided at its lower part with a plate, characterized in that said plate is positioned above the primary air inlet means, that plate provided with through holes being set up to receive the fuel without the fuel flowing through, and said burner further containing inside said cylinder means generating a partial vacuum in the burner, so as to create a primary air circulation from the bottom of said plate through the latter and the fuel resting on top up to a gas outlet duct in the upper part of said burner.
 2. Burner according to claim 1, characterized in that the means capable of creating a partial vacuum inside the burner consist of a compressed air feed means positioned in the upper part of the cylinder of the burner and generating a Venturi effect creating the partial vacuum.
 3. Burner according to claim 2, characterized in that the air from the Venturi effect also supplies the oxidant necessary for combustion in an outlet pipe of the burner.
 4. Burner according to claim 1, characterized in that the regular solid fuel supply means consist of a feed pipe engaged through an opening provided in the cylinder and connected to a fuel reserve by means of a rotary feeder which ensures the regular fuel supply.
 5. Burner according to claim 1, characterized in that the air inlet means consists of a space provided in the bottom plate of said burner, into which the air is fed.
 6. Burner according to claim 1, characterized in that it contains a means of scraping the bottom plate, also serving to even the fuel level so that the air will pass regularly.
 7. Burner according to claim 6, characterized in that it contains inside the cylinder a shaft, preferably tubular, which extends across the upper wall of the cylinder to the bottom wall, this shaft being rotatable at its end outside the cylinder, while its free end in the lower part of the cylinder is equipped with scraping means.
 8. Burner according to claim 7, characterized in that it contains means for translation drive of the shaft so as to lower the scraping means from its fuel spreading position to a position of contact with the plate, so that the scraping means will then serve to grind the residues present on the nozzle in order to make them pass the through holes of the nozzle.
 9. Burner according to claim 6, characterized in that it contains inside the cylinder a shaft, preferably tubular, which extends across the upper wall of the cylinder to the bottom wall, this shaft being driven rotatably at its end outside the cylinder, while its free end bears the bottom plate, which is thus driven in rotation with said shaft, the scraping means being mounted fixed in rotation in the cylinder.
 10. Burner according to claim 9, characterized in that the bottom plate preferably has a diameter roughly corresponding to the internal diameter of the cylinder, while the space constituting the air inlet means, provided under said bottom plate, has a greater diameter.
 11. Burner according to claim 9, characterized in that it contains means for translation drive of the shaft in order to lower the bottom plate in the space, thus freeing the periphery of the plate, the scraping means also being lowered with a wider amplitude, so that it abuts said bottom plate in its scraping position.
 12. Burner according to claim 11, characterized in that the bottom of the space is mounted pivoting on a pin, so as to open when the shaft, which is in one piece with said bottom, is lowered in order to lower the bottom plate, and so as to close when the shaft is raised again.
 13. Burner according to claim 11, characterized in that the shaft contains in its upper part outside the cylinder a pin extending crosswise to said shaft, that pin being mounted pivoting at one end, which is in a position lower than a pivot point of this pin on the shaft, lower in turn than the opposite end of the pin mounted at the end of the rod of a jack that is preferably pneumatic, the scraping means being borne by a shaft extending parallel to shaft and the end of which is mounted pivoting at on the pin in proximity to the end.
 14. Burner according to claim 1, characterized in that the primary air feed means consist of a pipe extending preferably centrally in the cylinder across the upper wall of the latter and entering under the plate of said burner through a central opening of sufficient section for the primary air.
 15. Burner according to claim 14, characterized in that the pipe is concentric to the shaft and surrounds the latter.
 16. Burner according to claim 1, characterized in that it further contains an outer casing defining with the cylinder an annular compartment in which the primary air is fed up to the air inlet means.
 17. Burner according to claim 7, characterized in that the rotary drive of the shaft is carried out simultaneously with the rotary feeder.
 18. Burner according to claim 7, characterized in that secondary air inlet means consisting of a pipe connected to primary air feed and/or inlet means extend into the cylinder and enter the upper part of the cylinder, so as to ensure a constant flame at the top of the burner at the level of the Venturi effect.
 19. Burner according to claim 1, characterized in that flame generating means, such as means of distribution of a gas such as propane or butane, are provided in the outlet pipe.
 20. Boiler for solid fuel such as biomass, having a burner, comprising a heating body in the form of a cylinder equipped with solid fuel feed means and primary air inlet means as oxidant, said cylinder being provided at its lower part with a plate, characterized in that said plate is positioned above the primary air inlet means, that plate provided with through holes being set up to receive the fuel without the fuel flowing through, and said burner further containing inside said cylinder means generating a partial vacuum in the burner, so as to create a primary air circulation from the bottom of said plate through the latter and the fuel resting on top up to a gas outlet duct in the upper part of said burner.
 21. Boiler according to claim 20, characterized in that the means of primary air feed from the boiler to the bottom of the burner are provided at the bottom of the boiler and consist of a pipe concentric to the gas outlets, which makes it possible to reheat the primary air and cool the outlet gases.
 22. Boiler according to claim 20, characterized in that contains a second stage of reheating of the return water from heating with the cooled gases of the first stage, a T-shaped gas outlet making it possible to take cooler gases at the bottom of the main body of the boiler, while the vertical part of the T-piece makes it possible to cool the cooler gases with water at lower temperature, a pipe enabling the water to be taken up at the top of the second heating body and to be injected in the bottom of the main body on the other side of a partition of the first stage of the boiler.
 23. Boiler according to claim 20, characterized in that it contains a boiler set up so that it can be positioned on the door of a standard type boiler. 